Method and device for cleanup and deposit removal from internal hot water system surfaces

ABSTRACT

Disclosed is a method of inhibiting and/or removing deposits from internal surfaces in a hot water system. The method includes controlling a real-time oxidation-reduction potential in a hot water system to alter the dynamic between deposit constituents and the bulk water of the system to inhibit deposition or initiate deposit removal. The method is equally effective for a system undergoing a wet layup sequence or in an online operational system. The invention further includes a multi-component deposit inhibition and/or removal device, including a receiver, a processor, and a transmitter that work in unison to alter the system dynamics to inhibit or remove deposits.

TECHNICAL FIELD

This invention relates generally to methods of inhibiting depositformation and removing deposits from internal surfaces of hot watersystems. More specifically, the invention relates to measuring real-timeoxidation-reduction potential at operating temperature and pressure inone or more operational protective zones and using those measurements tocontrol feed of active chemical species. The invention has particularrelevance to locally and/or globally inhibiting and/or removing depositsfrom internal surfaces in simple or complex hot water systems.

BACKGROUND

Hot water systems are generally composed of all-ferrous metallurgy ormixed metallurgy, such as copper or copper alloy systems, nickel andnickel-based alloys, and stainless steel and may also be mixed with mildsteel components. Many general classes/components of hot water systemsexist, such as boilers, hot water heaters, heat exchangers, steamgenerators, steam jackets and molds, nuclear power electric systemscombustion engine and diesel coolant systems, evaporator systems,thermal desalination systems, papermaking operations, fermentationprocesses, the like, and attached ancillary devices. They are dynamicoperating systems that undergo a myriad of REDOX Stress events (i.e.,any electrochemical event in the hot water system related to changes inoxidative or reductive state of the water). Such events generallyinclude any process that implicates the oxidation-reduction potential(“ORP”) space or regime in the system.

These events may result from a multitude of factors including speciesinherently found in the water, leaks from various components,contamination from air in-leakage, malfunctioning pumps, seals, vacuumlines, and gauges. Further, increased use of oxygen-enriched water, suchas boiler make-up water, returned steam condensate, and/or raw surfaceor subsurface water, deaerator malfunctions, steam and turbine loadswings, and problems with chemical feed pumps cause unplanned reductionor increase in chemical treatment feed rates. Uncontrolled REDOX Stressevents can cause serious general and localized corrosion problems, suchas pitting, stress corrosion cracking, corrosion fatigue, and/or flowaccelerated corrosion problems in hot water systems. By their nature,these problems tend to be electrochemical and thus tied-in to theoxidative-reductive properties of the environment and the structuralmaterial interaction.

Additional problems are encountered when plant equipment undergoesintermittent operations, including using steam in a periodic fashion.For example, a steam operated mold press in tire manufacturing orcomponents of a papermaking process may be in that category. In theextreme, steam system might be put into a layup sequence to either beidled (or slowed down) or started from idle to operating conditions. Amain concern is corrosion that occurs in situ followed by corrosionproduct transport to other plant locations during startup or shutdown ofthe intermittent process. Apart from the localized damage caused by insitu corrosion, the corrosion product transport can foul a multitude ofcomponents. Typically, the worst fouling occurs on the boiler tube wallswhere deposits can lead to poor heat transfer, increased boiler tubetemperatures, under-deposit corrosion, local overheating, and tubefailure. In situ corrosion and corrosion product transfer may alsoimpact the balance of the entire system, not just the boiler/steamgenerator. Impacted components may include transfer piping, holdingtanks, and ancillary equipment that come into contact with the hotwater/steam process fluids.

Although some conventional methods are practiced today to identify REDOXStress events in hot water systems, because of hot water system dynamicsmost REDOX Stress events are unpredictable. These methods are not widelypracticed because they have inherent drawbacks (see below). As aconsequence, the majority of REDOX Stress events go undetected and thusuncorrected. Uncontrolled REDOX Stress events can lead to seriouscorrosion and deposit problems in these systems, which negatively impactplant equipment life expectancy, reliability, production capability,safety, environmental regulations, capital outlay, and total plantoperation costs.

Identifying REDOX Stress events currently includes both onlineinstruments and grab sample wet chemical analysis test methods. In bothapproaches, the sample has to first undergo sample conditioning, such ascooling, prior to measurement. Examples of online instruments includedissolved oxygen meters, cation conductivity instruments, roomtemperature ORP instruments, pH instruments, sodium analyzers, hardnessanalyzers, specific conductivity meters, silica analyzers, particle andturbidity meters, reductant analyzers, and the like. General corrosionmonitoring, such as coupon and electrochemical analysis, is typicallyperformed after cooling a sample or at elevated temperatures. Grabsample test methods include analyzing for dissolved oxygen, pH,hardness, silica conductivity, total and soluble iron, copper, andsilica, reductant excess, and the like.

Some drawbacks of these methods include the following. Grab sampleanalysis gives a single point in time measurement and consequently isnot a viable continuous monitoring method for REDOX Stress events. Italso often has inadequately low-level detection limits. Online monitorsdo not provide a direct measurement of REDOX Stress and thus cannotindicate whether or not a REDOX Stress event is occurring at anyparticular time. Corrosion monitors detect general corrosion, but arenot capable of measuring changes in local corrosion rates or depositscaused by REDOX Stress events. Online reductant analyzers measure theamount of reductant, but not the net REDOX Stress a system is undergoingat system temperature and pressure. That REDOX Stress can occur in theapparent presence of a reductant is thus another drawback of thistechnique.

Dissolved oxygen (“DO”) meters have similar drawbacks. Measuring theamount of DO (an oxidant) but not necessarily the net REDOX Stress asystem is undergoing is not an accurate indicator of corrosion stress.The sample also must be cooled prior to DO measurement thus increasingthe lag time in detecting when the REDOX Stress event started. Further,the potential for oxygen consumption in the sample line could causeinaccurate readings. REDOX Stress can also occur in the apparent absenceof DO and little or no DO in the sample could potentially be a falsenegative. In addition, all of the instruments described above arerelatively costly to purchase, and require frequent calibration andmaintenance.

Corrosion coupons give a time-averaged result of general systemcorrosion. Again, this technique does not offer a real-time indicationor control of REDOX Stress events. Online electrochemical corrosiontools are inadequate for localized corrosion determinations and cannotbe used in low conductivity environments. Integrated metal samplingtechniques that use filtration to obtain a water sample on a cooledsample stream also provide no active real-time response with respect toREDOX Stress events.

Room temperature ORP is a direct measurement of the net ORP of a sampletaken from the system. A drawback of this technique is that it fails toindicate what is happening at system temperature and pressure. REDOXStress events that occur at operating temperature and pressure oftencannot be observed at room temperature, as process kinetics andthermodynamic vary with temperature. In addition, room temperature ORPmeasuring devices are more sluggish and more likely to become polarized.Reliability of such devices is poor and they need frequent calibrationand maintenance.

There thus exists an ongoing need to develop methods of inhibiting andremoving deposits from internal hot water system surfaces andcomponents, particularly by monitoring and controlling real-time ORP inhot water systems at operating temperature and pressure.

SUMMARY

A myriad of processes occurring in a hot water system contribute to theORP, which in turn acts as a REDOX Stress indicator for the hot watersystem. Adjustments to the ORP act to change the dynamic (e.g.,equilibrium constant) between constituents/components in a deposit on aninternal surface of the system and the water in the system. Suchadjustments may be used as a tool to inhibit and/or remove deposits(i.e., deposit control).

In contrast to conventional room temperature measurements, ORPmeasurements taken in real-time at system operating temperature andpressure (including at temperatures and pressures encountered duringintermittent operations, such as a layup process including, for example,a shutdown or startup sequence) are capable of indicating primary andsecondary REDOX Stress events occurring in the system in real-time. Suchreal-time ORP monitoring may be used to measure, identify, and assessREDOX Stress demands in the system and can act as a direct or indirectcorrosion process indicator. This invention accordingly provides amethod of monitoring and controlling ORP in a hot water system inreal-time at operating temperature and pressure to inhibit and/or removedeposits on internal surfaces in the system. It should be appreciatedthat the method has equal application in the steam producing equipment(i.e., boiler and/or boiler feed water), the steam usagehardware/components/equipment, the condensate zones, and/or other plantareas/components having an impact on plant balance.

In an aspect, this invention provides a method of inhibiting and/orremoving a deposit from an internal surface in a hot water system bycontrolling a real-time ORP at operating temperature and pressure in thehot water system. The operating temperature and pressure may varyconsiderably depending on whether the system is operational orundergoing a layup process. The method includes defining one or moreoperational protective zones (“zone” or “zones”) in the hot water systemand selecting at least one of the defined zones. One or more of theselected zones includes at least one ORP probe operable to measure thereal-time ORP and communicate with a controller. An ORP setting isassigned to one or more of the selected zones and one or more of theassigned ORP settings optimizes the dynamic between one or more depositconstituents to either inhibit deposition or cause release of at least aportion of the deposit into the water of the online hot water system.

In alternative embodiments, the real-time ORP is intermittently orcontinuously measured at one or more of the selected zones andtransmitted to the controller, which assesses whether the measuredreal-time ORP or a calculated ORP based upon the measured real-time ORPconforms to the optimized ORP setting. If the measured real-time ORP orthe calculated ORP does not conform to the optimized ORP setting, themethod includes taking action to affect the real-time ORP.

In an embodiment, the action including feeding an effective amount ofone or more active chemical species into one or more zones of the hotwater system. In another embodiment, the action includes altering systemtemperature to impact the real-time ORP. In alternative embodiments, theaction includes any mechanical, operational, or chemical process toimpact the real-time ORP and shift it into the desired ORP setting maybe instituted. Such action is intended to inhibit deposition and/orcause release of at least a portion of the deposit.

In another aspect, the invention includes a deposit inhibition and/orremoval device for a hot water system. The hot water system can be inany phase of a layup sequence or is online and operational and has oneor more zones, where a subset of the zones is selected zones. The devicealso includes a receiver that is in communication with one or more ORPprobes associated with one or more of the selected zones. A subset ofORP probes is activated and operable to measure a real-time ORP atoperating temperature and pressure in the hot water system. Inalternative embodiments, the operating temperature and pressure variesdepending upon whether the system is undergoing a layup sequence or isoperational. The device further includes a processor operable tointerpret the measured real-time ORP communicated to the receiver fromeach activated ORP probe.

In alternative embodiments, the processor interprets the measuredreal-time ORP directly and/or interprets a calculated ORP based upon themeasured real-time ORP. The interpreted ORP indicates a dynamic betweenone or more components in the deposit on an internal surface of the hotwater system and the water of the hot water system. To affect changes inthe dynamic, a preferred embodiment includes a transmitter incommunication with a feeding device operable to manage introduction ofone or more active chemical species into the hot water system. If theinterpreted real-time ORP does not conform to an optimized ORP setting,the processor is operable to send an output signal through thetransmitter to the feeding device. In another embodiment, thetransmitter is in communication with a temperature-altering mechanismoperable to initiate a sequence in one or more zones that impacts thereal-time ORP in the hot water system.

The optimized ORP setting relates to the ongoing dynamic of depositformation and/or release and suitable real-time ORP control inhibitsdeposition and/or effectuates release of at least a portion of thedeposit into the water of the hot water system.

In alternative embodiments, the ORP setting is either a same ORP settingfor each phase or a different ORP setting for at least two of thephases. The ORP setting may also be timed/ramped in a continuous orstepwise fashion to alter the real-time ORP in one or more zones.

It is an advantage of the invention to provide a method of inhibitingand/or removing deposits on internal surfaces of a hot water system byreacting to a real-time ORP by taking action to alter the real-time ORPby either feeding one or more active chemical species into the hot watersystem or initiating a temperature-altering sequence.

It is another advantage of the invention to provide a method ofinhibiting and/or removing deposits on internal surfaces of a hot watersystem undergoing a wet layup sequence by managing the sequence tomaintain an ORP setting in one or more operational protective zones.

A further advantage of the invention is to provide a hot water systemdeposit inhibition and/or removal device including a receiver, aprocessor, a transmitter, and a feeding or temperature-altering device,which work in unison to control a real-time ORP in one or moreoperational protective zones during a plurality of layup sequence phasesin the hot water system.

An additional advantage of the invention is to provide a hot watersystem deposit inhibition and/or removal device including a receiver, aprocessor, a transmitter, and a feeding device, which work in unison tocontrol a real-time ORP in one or more operational protective zones inan online and operational hot water system.

Another advantage of the invention is to increase hot water systemefficiency during layup by enabling improved maintenance and control ofsystem parameters thus allowing quicker recovery from layup.

Yet another advantage of the invention is to optimize operating costsfor a variety of hot water systems and components by accuratelyinhibiting and/or removing internal deposits.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description, Examples, andFigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified 3-component hot water system, where make-upwater flows through a “Deaerator,” a “FW Pump,” and into a “Boiler” andthe boiler in turn generates “Useful Steam” for subsequent use invarious processes.

FIG. 2 illustrates a more complex boiler configuration, including aplurality of feed water pumps, a plurality of heat exchangers, and asteam producer.

FIG. 3 depicts various “ORP Control Zones,” where the ORP setting may bedifferent for systems at various temperatures.

FIG. 4 illustrates feeding multiple REDOX active species at variouslocations to control the @T ORP at a single location.

FIG. 5 illustrates that one or more ORP probes may be positioned in anyof a multitude of locations for a layup sequence.

FIG. 6 shows various “ORP Control Zones for Layup” and examples of ORPsettings for each phase of the layup sequence.

DETAILED DESCRIPTION

Hot water systems are often not continuously operated. Betweenoperational cycles, these systems typically undergo a layup sequence tobring them offline and into an idle mode. Special considerations need tobe made to remove and/or inhibit deposits on internal surfaces while ahot water system is online and operational, which may includeintermittent operational phases, such as an entering shutdown phase, ashutdown phase, an exiting shutdown phase, and an operational phase.Required concentrations of active chemical species can be higher duringintermittent operations (sometimes one or more orders of magnitude) thanduring normal hot water system operation. By monitoring real-time ORP atoperating temperature and pressure (which varies depending upon theparticular stage) it is possible to fine-tune and control the ORP spaceduring each phase of full operation and/or intermittent operation (e.g.,layup sequences). It is contemplated that this monitoring may be used onits own or in concert with one or a multitude of other monitor and/orcontrol tools.

The following definitions are not intended to limit the scope of theinvention. The defined terminology is for the purpose of describingparticular embodiments only and for providing guidance in interpretingthose descriptions. This invention will be limited only by the appendedclaims and equivalents thereof.

“Active chemical species” refers to oxidants, reductants,corrosion-inhibitors, corrodants, and other species that have an affecton or influence the ORP (and thus the dynamic (e.g., equilibriumconstant or other dynamics) between internal deposit constituents andthe system water) in a hot water system. Such species are described inmore detail below.

“Controller system,” “controller,” and similar terms refer to a manualoperator or an electronic device having components such as a processor,memory device, digital storage medium, cathode ray tube, liquid crystaldisplay, plasma display, touch screen, or other monitor, and/or othercomponents. In certain instances, the controller may be operable forintegration with one or more application-specific integrated circuits,programs, computer-executable instructions, or algorithms, one or morehard-wired devices, wireless devices, and/or one or more mechanicaldevices. Some or all of the controller system functions may be at acentral location, such as a network server, for communication over alocal area network, wide area network, wireless network, Internetconnection, microwave link, infrared link, and the like. In addition,other components such as a signal conditioner or system monitor may beincluded to facilitate signal-processing algorithms.

“Hot water system,” “system,” and like terms refer to any system wherehot water is in contact with metallic surfaces. “Hot water” means waterhaving a temperature from about 37° C. up to about 370° C. The systemmay operate at or below atmospheric pressure or a pressure up to about4,000 psi. Systems undergoing a layup sequence or a laid-up system willtypically have a lower temperature than a fully operational system;however, the encountered temperatures are generally well above ambient.In cases where intermittent operations occur and layup durationincreases, encountered temperatures may transition or approach ambienttemperatures.

“Layup” refers to discontinuing steam-producing operations for short orlong periods, including processes that do not continuously use hot wateror produced steam.

“ORP,” “@T ORP™ (a Nalco Company® trademark),” “at-T ORP,” and“real-time ORP” refer to oxidation-reduction potential for an industrialwater system at operating temperature and pressure. In certain instancesherein, ORP is indicated as room temperature ORP.

“ORP probe” refers to any device capable of measuring and transmitting areal-time ORP signal. Though any suitable device may be used, apreferred device is disclosed in U.S. patent application Ser. No.11/668,048, entitled “HIGH TEMPERATURE AND PRESSURE OXIDATION-REDUCTIONPOTENTIAL MEASURING AND MONITORING DEVICE FOR HOT WATER SYSTEMS,” whichis incorporated herein by reference in its entirety. Typically, the ORPprobe includes a temperature detector, a noble metal electrode, and areference electrode.

“REDOX Stress” refers to any electrochemical event in a hot water systemrelated to changes in oxidative or reductive potential, either directlyor indirectly.

In one embodiment, the method includes an automated controller. Inanother embodiment, the controller is manual or semi-manual, where anoperator interprets the signals and determines feed water (“FW”)chemistry, such as oxygen or other oxidant, oxygen scavenger or otherreductant, corrosion-inhibitor, and/or corrodant dosage. In anembodiment, the measured ORP signal is interpreted by a controllersystem that controls FW chemistry according to the described method. Inan embodiment, the controller system also interprets measuredtemperature to determine the amount of active chemical to add, if any.The temperature detector might also be used for information purposes,such as in alarm schemes and/or control schemes. It should beappreciated that the control scheme may incorporate pump limiters,alarming, intelligent control, and/or the like, based off furtherinputs, such as pH, DO levels, and other water constituents/properties.

It is contemplated that the disclosed method is applicable in a varietyof hot water systems, including both direct and satellite activechemical feeding designs and including any number of phases in theoperational and layup sequences. “Direct” feeding typically refers tomeasuring real-time ORP at a zone and feeding active chemical to thesame zone. “Satellite” feeding usually refers to measuring real-time ORPat a zone and feeding active chemical to a different zone. Inalternative embodiments, any zone may be associated with any layup phaseand the zones used during a particular phase may differ from zones usedduring another phase.

Representative systems and system components include condensers, bothtube and shell side; heat exchangers; pumps; seals; mild steel orcopper-based FW heaters; copper-based alloy surface condensers;deaerators; water tube and fire tube boilers; paper machines; condensatereceivers; steam condensate transfer lines with or without steam traps;process liquid heat exchangers; evaporators; desalination systems;sweet-water condensers; attemperated water sources; flow-acceleratedcorrosion protection; air heaters; engine coolant systems for diesel andgasoline; injection molds and other molding devices; and the like.

Other exemplary processes include papermaking process, such as Kraftpulping and bleaching processes; wafer polishing and planarizationprocesses (e.g., silicon wafer polishing); combustion gas emission(e.g., SO₂, NO_(X), mercury); fermentation processes; geothermalprocesses; tire molding processes; and aqueous organic redox synthesis(i.e., polymerization processes that require redox initiators).

Conventional corrosion control regimes use one point feed. The disclosedinvention uses targeted feed by precisely determining the needed activechemicals and the proper amount/dosage of those chemicals. Such targetedfeed is highly effective in removing internal deposits. For example,relatively oxidizing zones, such as low-pressure FW heaters(copper-based metallurgy), and more reducing zones, with high-pressureFW heaters (non copper-based metallurgy), may be differentiated toalleviate flow-accelerated corrosion-related issues. Relativelyoxidizing conditions within all ferrous FW heaters at sections ofpressurized water reactors versus relatively reducing final FW heaterregimes for stress corrosion cracking mitigation in steam generators.

The invention is capable of detecting and reacting to both primary andsecondary REDOX Stress events to inhibit and/or remove internaldeposits. Typically, the implementer knows the system implications andpossible REDOX stressors and is able to accordingly select one or moreof the defined operational protective zones to appropriately monitor agiven system's @T ORP space. In this way, it is possible to inhibitand/or remove deposits from an online and operation system or during anyphase of the layup sequence by feeding REDOX active species based offlocal and/or remote @T ORP readings as a primary REDOX Stress indicator.The @T ORP space is monitored and measured to assess and identify systemdemands, which are then compared to known/formulated metrics to react,solve, and control REDOX Stress events. As an indicator of secondaryREDOX Stress, the invention can detect processes resulting from prior,primary REDOX Stress, where the primary REDOX stressor is no longerevident.

The ORP probe may detect several different factors that contribute toREDOX Stress events in the hot water system. For example, an ORP probein a selected zone for a given phase can act as a direct indicator ofreal-time ORP in that zone or in another zone. In an embodiment, thereal-time ORP is measured in a first selected zone and one or moreactive chemical species are fed to the first selected zone, if themeasured real-time ORP at the first selected zone or the calculated ORPdoes not conform to the optimized ORP setting for the first selectedzone. In another embodiment, the real-time ORP is measured at a firstselected zone and one or more active chemical species are fed at one ormore other selected zones, if the measured real-time ORP or thecalculated ORP does not conform to the optimized ORP setting for thefirst selected zone. In a further embodiment, one or more real-time ORPsare measured at one or more of the selected zones and one or more otherreal-time ORPs are calculated for one or more other selected zones,based upon one or more of the measured real-time ORP(s).

As described above, in some cases, the measured ORP in a first zone isused to calculate an ORP for another zone. Such calculations may be doneby making various assumptions regarding system dynamics or by measuringtemperature/water chemistry differences between zones. Using mixedpotential theory and thermodynamic/kinetic principles known to thoseskilled in the art also allows for approximating conditions in otherzones. However, such calculations are typically subject to inherentinaccuracies; thus, the preferred method is to measure the real-time ORPin situ in selected zones.

Several important factors exist for determining or defining specificoperational protective/control zones for a system for an online andoperational system or for any phase of the layup sequence or process.The goal for any particular system is to achieve @T ORP “Plant SpecificBoiler Best Practices” for that system. For instance, certain plants arelimited to certain chemistries due to control philosophy, environmentalconstraints, economics, industry standards, etc. System temperaturesalso may dramatically vary from one plant to another, which requiresadjusting the specific control philosophy employed, explained in moredetail in the below Examples. Different plants may also have a uniqueREDOX Stress baseline and insipient changes to the baseline may need tobe determined.

Other factors include, specific ORP altering species purposefully addedor insipiently present; engineering alloys of construction for variousportions/entities in the system; desired general and local corrosionmitigation; dosing limitations; other system design specifics; specialconsiderations, such as flow-accelerated corrosion, stress, andcorrosion cracking; system variability. Those skilled in the art wouldunderstand how to assess these and other system variables/specifics toimplement the invention for a specific plant or system.

Ideally, any portion of a plant can have its @T ORP REDOX Stressmeasured and controlled using @T ORP. That is, the REDOX active speciesis fed directly to a specific piece of equipment (or group of equipment)and the @T ORP of the water in that piece of equipment is measured insitu and controlled for deposit inhibition/removal. This invention morespecifically addresses internal deposits local to the part(s) beingprotected and transport of deposit and corrosion products withconcomitant deleterious effects of that corrosion transport elsewhere inthe system, including fouling, heat transfer surface coating, turbinedeposition, etc. This type of full equipment monitoring and controlapproach is often not possible due to system limitations and economics.As such, parts of systems typically need to be handled as wholeentities. In some cases, the entire feed water train of a boiler systemmight be the entity. Alternatively, only small portions of the system orgroups of portions of the system are the entity. For example, thecondensate associated with a single paper machine or a single boiler. Itis contemplated that any portion, component, or entity (including theentire system viewed as one entity) may be selected andmonitored/controlled in any phase of the layup process or in an onlineoperational system.

In an aspect, the optimized ORP setting for one selected zone mayoverlap with another defined or selected zone. In another aspect, theoptimized ORP setting for one selected zone is completely independent ofeach and every other defined or selected zone. In a further aspect, theoptimized ORP setting for one selected zone is partially dependent uponfactors in one or more other defined or selected zones. In anembodiment, the optimized ORP setting is determined for a first selectedzone and additional ORP settings are optionally determined foradditional selected zones, if any. In one embodiment, each additionaloptimized ORP setting is independently determined. Alternatively, one ormore of the optimized ORP settings may be dependent upon one or moreother optimized ORP settings. Optimized ORP settings are generallydependent and based upon operational limitations of the hot watersystem. Such overlap or independence of the ORP setting likewise appliesfor each phase of the layup process and for online operational systems.

Determining the ORP setting for any particular system may beaccomplished by any suitable method. A preferred method is described inU.S. patent application Ser. No. 11/692,542, entitled “METHOD OFINHIBITING CORROSION IN INDUSTRIAL HOT WATER SYSTEMS BY MONITORING ANDCONTROLLING OXIDANT/REDUCTANT FEED THROUGH A NONLINEAR CONTROLALGORITHM,” which is incorporated herein by reference in its entirety.It is contemplated, however, that any method known to those skilled inthe art may be employed to ascertain the ORP setting for each phase andfor each zone. Such methods may include using experimental data,empirical knowledge, theoretical calculations, or any other suitablemethod.

In an embodiment, the ORP setting is an ORP set point that is chosenfrom one or more single values. In another embodiment, the ORP settingis an ORP set range chosen from one or more ranges of values. Over time,the ORP setting for any selected zone may be adjusted or changed. Forexample, a given plant may have a timetable outlining ORP settings fordifferent parts/components of the system at different times. Thistimetable would typically be based upon operational factors in thesystem that may change as demands on the system change.

Some zones might be kept relatively reducing and other zones might berelatively more oxidizing. For example, referring to FIG. 2, HeatExchangers 1 and 2 might be manufactured from an alloy that exhibits lowcorrosion rates under more reducing conditions. Whereas, Heat Exchanger3 might be manufactured from a different metallurgy that exhibits lowercorrosion rates under more oxidizing conditions. The “Steam Producer”might then again need to be kept under more reducing conditions. The @TORP control zones would be accordingly adjusted and monitored tocompensate for these differences. Moreover, different parts of the plantmight be subject to varying levels of corrosion and internal deposits.

In one embodiment, one or more of the selected zones may be in amonitoring and/or alarm mode, while one or more other selected zones isin a control mode. A selected zone in a monitoring and/or alarm mode iscapable, in an embodiment, of switching between these modes. Suchswitching may either be manually controlled or automatic. Severalexamples are presented below of how @T ORP system design can be used forREDOX stress control.

In another embodiment, the @T ORP is measured across any pump to detectpump or seal corrosion or failure. In another embodiment, the method maybe used to detect heat exchanger tube leaks as one active chemicalspecies might transfer through the leak in the heat exchanger to theother side (e.g., shell side to tube side or visa versa). Anotherexample would be a surface condenser cooling water leak into a FWcondensate hot well. In a further embodiment, the method may be used todetect any unwanted intrusion of external active chemical species (i.e.,system contaminants). In an alternative embodiment, @T ORP can be usedto form a “fingerprint” of specific REDOX stressors in a system. In thisway, it can be used as an early warning system for boiler tube ruptureas more boiler makeup water is added to the system from time to timewith a concomitant increase in the REDOX stress and possible internalsystem deposits.

Measured or calculated ORP values may indicate amounts ofelectrochemically active species in one or more of the selected zones.Such an indication may either be directly seen in the zone where the ORPwas measured or inferred in another zone where the ORP was not directlymeasured. In certain cases, the measured or calculated ORP indicates anamount of chemical that indirectly affects an amount ofelectrochemically active species in one or more selected zones. In amore typical case, the electrochemically active species directlyinfluences the measured or calculated ORP.

In one embodiment, the method includes ramping from one of the selectedzones to another one of the selected zones after a triggering event Anyevent that causes a shift or change in the real-time ORP in one or morecontrol zones may be a triggering event, such as a time-activatedtrigger or a temperature-activated trigger. According to an embodiment,a triggering event may be switching from one phase to another phase ofthe layup process in one or more parts of the system. A person havingordinary skill in the art would be able to analyze such options andchoose one or more triggering events for a system. For instance,bringing pumps or other parts of the system online (or taking offline)may be a triggering event as well as switching between parts/entities ofthe system to inhibit/remove deposits in each respective part/entity.Steam pressure changes due to downstream use changes, such as betweenturbine driving and other lower pressure uses, may also be chosen as atriggering event.

Triggering may also be based on activating or deactivating variouscondensate streams, which could introduce specific REDOX stressors inthe system. Such triggering events could be detected by probes, relays,monitors, etc., while remaining detectable by changes in the real-timeORP in one or more control zones. Moreover, the rate of change of theseand other events may dictate the ramping rate from one control zone toanother control zone, including instantaneous, timed, stepwise, or othersuitable ramping modes.

Representative triggering events may also include numerous timedoperations or timetables or other plant dynamics. A timetable could be afixed startup time followed by ramp up in some system operations overtime. For example, 30 minutes after initiating FW flow, the real-timeORP should be within 100 mV of the desired ORP setting. After 20 minutesof full load firing of the boiler, the real-time ORP should be ramped upto the ORP setting. The ramping may also be triggered when an ORPsetting has been achieved elsewhere in the system, such as upstreamcomponents. For example, once an upstream control zone has achieved itsORP setting (or is within, for instance, 50 mV), a downstream controlzone is activated or brought into a control mode. Such sequencing ofreal-time ORP control is one preferred method of sequentiallyinhibiting/removing deposits from internal system entity surfaces.

Changing plant dynamics may also initiate triggering and/or ramping.Such dynamics can change rapidly during a layup process. In anembodiment, the triggering event includes plant power output changes.For example, a 5% power output decrease may be the triggering event thatinitiates real-time ORP changes in one or more control zones in thesystem. The procedure used to initiate the real-time ORP changes mightbe, for example, an immediate signal to change the ORP setting for oneor more control zones or a gradual ramp to a new ORP setting. Thisprocedure may be based upon the rate or magnitude of power decline.Furthermore, the triggering and/or ramping mechanisms might be complexinterconnections of multiple signals and timing.

In a preferred embodiment, changes and adjustments to FW chemistry (orchemistry in any part or entity of the hot water system) includes addingoxygen or other oxidant, oxygen scavenger or other reductant,corrosion-inhibitor, corrodant, and/or other active chemicals to the FW.By definition, oxygen scavengers are reducing agents, although not allreducing agents are necessarily oxygen scavengers. Reducing agents,suitable as oxygen scavengers, satisfy the thermodynamic requirementsthat an exothermic heat of reaction exists with oxygen. For practicalapplications, reasonable reactivity is typically required at lowtemperatures. That is, there should be some favorable kinetics ofreaction to initiate deposit removal. Furthermore, other changes andadjustments to FW chemistry, such as for system control and corrosioncontrol may include adding other oxidizing agents (oxidants), otherreducing agents (reductants), and/or other active or inert chemicals.

It is also highly desirable that the reducing agent and its oxidationproducts are not corrosive and do not form products that are corrosivewhen they form in steam generating equipment. Typically, certain oxygenscavengers function optimally in certain pH ranges, temperatures, andpressures and are also affected by catalysis in one way or another. Theselection of the proper oxygen scavengers for a given system can bereadily determined based on the criteria discussed herein and knowledgeof those skilled in the art.

Preferred reductants (i.e., oxygen scavengers) include hydrazine,sulfite, bisulfite, carbohyrazide, N,N-diethylhydroxylamine,hydroquinone, erythorbate or erythorbic acid, methyl ethyl ketoxime,hydroxylamine, tartronic acid, ethoxyquin, methyltetrazone,tetramethylphenylenediamine, semi-carbazides, diethylaminoethanol,monoethanolamine, 2-ketogluconate, ascorbic acid, borohydrides,N-isopropylhydroxylamine, gallic acid, dihydroxyacetone, tannic acid andits derivatives, food-grade antioxidants, the like, and anycombinations. It should be appreciated that any active chemical speciesmay be used in the method of the invention.

Representative oxidants include oxygen, hydrogen peroxide, organic(alkyl and aryl) peroxides and peracids, ozone, quinone, acid and baseforms of nitrates and nitrites, the like, and combinations.

Representative corrodants include mineral acids (e.g., HCl, H2SO4, HNO3,H3PO4) and their salts/derivatives; caustics (e.g., Na, K, Li,hydroxides); ammonium hydroxide; chelants, such as EDTA, NTA, HEDP;phosphonic acid and polyphosphonic acids; phosphonates; water solubleand/or dispersible organic polymeric complexing agents, such as acrylicacid homopolymers, copolymers, and terpolymers; acrylamide;acrylonitrile; methacrylic acid; styrene sulfonic acids; the like; andcombinations.

Representative corrosion inhibitors include alkali and amine salts ofphosphate and polyphosphates; neutralizing amines; molybdates;tungstates; borates; benzoates; filming inhibitors, such as alkyl,alkenyl, and aryl polyamines and their derivatives; surfactantcompositions, such as that disclosed in U.S. Pat. No. 5,849,220;oligomeric phosphinosuccinic acid chemistries, such as that disclosed inU.S. Pat. No. 5,023,000; the like; and combinations.

EXAMPLES

The foregoing may be better understood by reference to the followingexamples, which are intended for illustrative purposes and are notintended to limit the scope of the invention.

Example 1

FIG. 1 depicts a simplified 3-component hot water system. Make-up waterflows through a “Deaerator,” a “FW Pump,” and into a “Boiler.” Theboiler in turn generates “Useful Steam” that is used for variousdownstream processes. In this Example, ORP may be monitored/controlledat the Deaerator exit, labeled as “1” in FIG. 1, or at the FW Pump exit,labeled as “2” in FIG. 1. REDOX Stress may be reacted to in real-time asit occurs in the Deaerator and/or FW Pump independently. Active chemicalspecies may also be fed into the Deaerator, after the Deaerator, and/orafter the FW Pump for more specific corrosion control. While suchadjustments to the real-time ORP typically occur during normalsteady-state operation, intermittently operated systems or systemsundergoing a layup sequence equally benefit from this deposit controlregime.

Example 2

FIG. 2 illustrates a more complex boiler configuration, including aplurality of feed water pumps, a plurality of heat exchangers, and asteam producer (i.e., boiler). In such a configuration, any number(i.e., one, two, or more) of condensers, heat exchangers, pumps,boilers, process steam applications, etc. could be used. In FIG. 2,flowing feed water is shown as solid arrowed lines as it moves towardthe “Use of Process Steam” areas 1 and 2. Condensed steam is shown asdotted arrowed lines as it is fed to various plant locations, whichcould include the shell side of heat exchangers or directly back to thecondensate areas. If desired, condensate that does not meet plant waterspecifications for boiler feed water could be drained out of the systemas blow down.

Examples of positions where ORP could be monitored/controlled and/orfeed locations for active chemical species are labeled as “22” in FIG.2. Such user-controlled positioning allows local depositinhibition/removal capabilities for a specific units and/or groups ofunits as well as global deposit control. While such adjustments to thereal-time ORP typically occur during normal steady-state operation,intermittently operated systems or systems undergoing a layup sequenceequally benefit from this deposit control regime.

Example 3

FIG. 3 depicts how the ORP setting may be different for systems atdifferent temperatures. The temperatures shown in FIG. 3 may represent,for example, different plants or different operationalprotective/control zones in the same plant. In this Example, the ORPsetting is an ORP set range selected from a series of ranges, shown asvertical lines labeled “Preferred,” “Broader,” and “Broadest.” Dependingupon the sophistication of equipment in the plant (i.e., operationallimitations), the useable ORP set range or point may vary. That is, someplants are able to handle a narrow, or preferred, ORP set range, whereasother plants are able to handle only a broader ORP set range.

The @T ORP numbers would typically be recorded against an externalpressure balanced reference electrode (designated as “EPBRE” in FIG. 3)having 0.1 normal potassium chloride filling solution. The first 180° F.control zone might be measured and controlled by an @T ORP probepositioned after “Heat Exchanger 2” (FIG. 2) in the feed water, and theactive chemical species might be fed into the feed water just after the“Condenser” (FIG. 2) in the feed water.

The second 350° F. control zone might be measured and controlled by an@T ORP™ probe positioned after “Heat Exchanger 3” (FIG. 2) in the feedwater, and the active chemical species might be fed into the feed waterjust prior to “Heat Exchanger 3” (FIG. 2) in the feed water.

The third 500° F. control zone might be measured and controlled by an @TORP™ probe positioned after “Heat Exchanger 4” (FIG. 2) in the feedwater, and the active chemical species might be fed into the feed waterjust prior to “Heat Exchanger 4” (FIG. 2) in the feed water.

Example 4

This Example illustrates feeding multiple REDOX active species atvarious locations to control the @T ORP at a single location, as shownin FIG. 4. The controlling @T ORP probe was placed directly upstream ofthe feed location for REDOX active species #2. The @T ORP probe was usedto measure the @T ORP prior to the feed of REDOX active species #2. The@T ORP probe was then switched to control the feed of another REDOXactive species (#1), being fed upstream of the single @T ORP probe. Itshould be noted that when REDOX active species #2 (that was beingmanually controlled) was turned off, the effect of that loss quicklypermeated the plant water chemistry and was sensed by the @T ORP probe.The controller (in this Example, the controller was automated for REDOXactive species #1) immediately initiated additional feed of REDOX activespecies #1 to make-up for the shortfall in REDOX active species #2.

The controlled feed of REDOX active species #1 was able to achieve andmaintain the @T ORP setting thus maximizing deposit control in the heatexchangers during this event. Note that as soon as the REDOX activespecies #2 was manually turned back on, the deposit control device(i.e., the @T ORP probe system) immediately compensated by cutting feedof REDOX active species #1 to maintain the desired @T ORP setting fordeposit control.

Example 5

This Example illustrates an unpredicted response of the @T ORP probe tomeasure corrosion events directly and how real-time ORP measurements actas a direct indicator of deposit formation tendency in hot water systemsfrom REDOX Stress events.

The @T ORP probe reacts to the formation of corrosion products (i.e.,potential deposit constituents) in the FW. The REDOX stresses in the FWinclude contributions from complex conjugate ionic corrosion pairs likeFe2+/Fe3+ or Cu+/Cu2+, for example. In an all iron-based FW heater,water of high DO (i.e., greater than 500 ppb) starts to enter the FWheater. The room temperature ORP and real-time ORP at the heater inletwere initially −125 mV and −280 mV, respectively. On experiencing theadded REDOX stress event, the room temperature ORP and real-time ORP atthe heater inlet rose to −70 mV and −30 mV, respectively. Thesensitivity of the @T ORP probe (real-time ORP increases 250 mV) isclearly seen as compared to the room temperature ORP probe (increasedonly 55 mV). The real-time and room temperature ORP probes at the FWheater exit were initially −540 mV and −280 mV, respectively. After thehigh REDOX stress event the real-time and room temperature ORP probes atthe FW heater exit became −140 and −280 mV, respectively. It isimportant to note that the real-time ORP rose by 400 mV, whereas theroom temperature ORP showed no change.

It is not intended to be bound to any particular theory; however, onetheory that the room temperature ORP measurements at the exit of the FWheater showed no change was that the DO exiting the FW heater remainedunchanged throughout the DO ingress event at the inlet of the FW heater.The reason the real-time ORP numbers rose so dramatically at the FWheater exit was most likely because of the corrosion that had occurredin the FW heater itself. This event generated a plentiful supply ofionic oxidized iron species, which the @T ORP probe detected, but theroom temperature ORP probe did not.

The same effect was seen across copper based FW heaters where thedissolved oxygen was consumed within the FW heaters. Once again, roomtemperature ORP measurements showed no change at the exit of the FWheaters, but @T ORP probe responses showed elevated numbers as oxidizedcopper ionic species (conjugate pairs) were released into the FW andexited the FW heater, only to be sensed by the @T ORP probes and not theroom temperature ORP instruments.

Example 6

This Example illustrates that @T ORP probe positioning could be in anyone or multiple of locations, labeled as “22” in FIG. 5. The real-timeORP could be measured at one or more locations within the component, inwater entering or exiting the component, or at the inlet and/or outletof a pump used to recalculate layup water ORP values in the component.REDOX active species could be fed into the component at any suitablelocation (or other location) to keep the @T ORP at a desired ORP settingfor any phase of the layup process. In an embodiment, the ORP settingvaries during the layup process. Alternatively, the ORP setting does notvary.

Example 7

FIG. 6 shows a representative scenario for layup process ORP control,where a time sequence is presented as a component (or groups ofcomponents) go from operational use through layup and back to systemoperation. In this case, the @T ORP control zone might be furtherreduced while “Entering Layup,” and more positive “During Layup.” Thisdifference is primarily due to the lower temperatures experienced inlayup. In the “Exiting Layup” phase the system is made more reducing andthe @T ORP setting drops further as system temperatures increase.

Example 8

This Example illustrates using real-time ORP measurement for onlinecleanup of heat transfer surfaces in a hot water system. A plant thathad been operating using the @T ORP controlled feed of oxygenscavenger/reductant/metal passivator typically required several days tostartup as it was limited by iron, copper, and silica loading (i.e.,internal deposits) in the boiler. After being on the @T ORP program forjust 5 months, these limitations were no longer an issue at startup. Theplant was only limited in how fast it could thermally load the boiler (5to 6 hours in this case), before it was back to full system load.

Reducing FW corrosion, in turn reduces deposits of corrosion products inthe boiler and lowers corrosion product transport on startup. Boilerwater suspended solids were lower at start up, thus eliminating pressureholds for total suspended solids reduction, prior to regaining fullpower. Lower metals transport during plant operations usually leads tolower entrapment or hideout (e.g., silica and phosphate) in the boilerand ultimately release during start up. For example, dirty boilers willcleanup as deposited material moves from the coated tube surfaces to thebulk water, which would have extremely low corrosion product suspension.This material then has the opportunity to go from tube surfaces to thebulk water and ultimately out with the boiler blowdown.

It should be understood that it will be apparent to those skilled in theart various changes and modifications to the described embodiments. Suchchanges and modifications can be made without departing from the spiritand scope of the invention and without diminishing its intendedadvantages. It is therefore intended that such changes and modificationsbe covered by the appended claims.

1. A method of inhibiting and/or removing a deposit from an internalsurface in a hot water system by controlling a real-timeoxidation-reduction potential (“ORP”) at operating temperature andpressure in the hot water system, the method comprising: (a) definingone or more operational protective zones (“zone” or “zones”) in the hotwater system; (b) selecting at least one of the defined zones, whereinone or more of the selected zones includes at least one ORP probeoperable to measure the real-time ORP and communicate with a controller;(c) assigning an ORP setting to one or more of the selected zones; (d)optimizing one or more of the assigned ORP settings to inhibitdeposition or to cause release of at least a portion of the deposit intothe water of the online hot water system; (e) either intermittently orcontinuously measuring the real-time ORP at one or more of the selectedzones; (f) transmitting the measured real-time ORP to the controller;(g) assessing whether the measured real-time ORP or a calculated ORPbased upon the measured real-time ORP conforms to the optimized ORPsetting; and (h) taking action to change the real-time, if the measuredreal-time ORP or the calculated ORP does not conform to the ORP setting,wherein said action optionally includes feeding an effective amount ofone or more active chemical species into the hot water system oraltering the temperature of one or more zones in the hot water system toinhibit deposition or to cause release of at least the portion of thedeposit.
 2. The method of claim 1, wherein the hot water system is inany phase of a layup sequence or is online and operational.
 3. Themethod of claim 1, wherein the ORP probe includes a temperaturedetector, a noble metal electrode, and a reference electrode.
 4. Themethod of claim 1, including optimizing the ORP setting to affect adynamic between a component in the deposit and the component in thewater of the hot water system to inhibit deposition or to cause releaseof at least the portion of the deposit into the water of the hot watersystem.
 5. The method of claim 1, wherein the optimized ORP setting isselected from the group consisting of: an ORP set point chosen from oneor more single values; an ORP set range chosen from one or more rangesof values; and an ORP set range including a series of successivelysmaller ranges.
 6. The method of claim 1, wherein the optimized ORPsetting is a same optimized ORP setting for each selected zone or adifferent optimized ORP setting for at least two of the selected zones.7. The method of claim 1, including independently determining the ORPsetting for one or more of the selected zones based upon operationallimitations of the online hot water system.
 8. The method of claim 1,wherein at least one of the selected zones is in a monitoring and/oralarm mode and at least one other selected zone is in a control mode. 9.The method of claim 8, wherein at least one of the selected zones iscapable of switching between the monitoring and/or alarm mode and thecontrol mode.
 10. The method of claim 1, including measuring thereal-time ORP at a first selected zone and feeding one or more activechemical species to the first selected zone, if the measured real-timeORP or the calculated ORP does not conform to the optimized ORP settingfor the first selected zone; or measuring the real-time ORP at a firstselected zone and feeding one or more active chemical species at one ormore other selected zones, if the measured real-time ORP or thecalculated ORP does not conform to the optimized ORP setting for thefirst selected zone.
 11. The method of claim 1, including automaticallyfeeding the active chemical species.
 12. The method of claim 1,including manually feeding the active chemical species.
 13. The methodof claim 1, wherein the active chemical species is selected from thegroup consisting of: oxidants, reductants, corrosion-inhibitors,corrodants, and combinations thereof.
 14. The method of claim 1, whereinthe released portion of the deposit exits the hot water system asblow-down.
 15. The method of claim 1, wherein the deposit is selectedfrom the group consisting of: hard scale, soft scale, silica,phosphates, entrapped organic material, corrosion products, andcombinations thereof.
 16. The method of claim 1, including operating themethod over a network.
 17. The method of claim 16, wherein the networkis an Internet.
 18. A digital storage medium having computer-executableinstructions stored thereon, the instructions operable to execute themethod of claim
 1. 19. The method of claim 1, wherein the hot watersystem is selected from the group consisting of: fossil fuel firedwater-tube or fire-tube boilers; hot water heaters; heat exchangers;steam generators; nuclear power electric systems including light waterreactors, pressurized water reactors, and boiling water reactors; marineunits; combustion engine and diesel coolant systems; evaporator systems;thermal desalination systems; evaporator systems; papermaking operationsincluding pulping processes and bleaching processes; condensate systems;wafer polishing and planarization processes; combustion gas emissions;molding processes; fermentation processes; geothermal processes; aqueousorganic redox synthesis; polymerization processes; steam ejectionequipment; processing operations; and ancillary devices attachedthereto.
 20. A deposit inhibition and/or removal device for a hot watersystem, wherein the hot water system is in any phase of a layup sequenceor is online and operational, the online hot water system having one ormore operational protective zones (“zone” or “zones”), wherein a subsetof the zones are selected zones, the device comprising: a receiver incommunication with one or more oxidation-reduction potential (“ORP”)probes, a subset of the ORP probes being activated, each activated ORPprobe operable to measure a real-time ORP at operating temperature andpressure in the hot water system, and one or more of the selected zonesincluding at least one ORP probe; a processor operable to interpret themeasured real-time ORP communicated to the receiver from each activatedORP probe, wherein the processor either interprets the measuredreal-time ORP directly or interprets a calculated ORP based upon themeasured real-time ORP, and wherein the interpreted ORP indicates adynamic between one or more components in said deposit on a surface ofthe hot water system and the water of the hot water system; and atransmitter in communication with a feeding device operable to manageintroduction of one or more active chemical species into the hot watersystem to affect changes in the dynamic, wherein the processor isoperable to send an output signal through the transmitter to the feedingdevice, or wherein the transmitter is in communication with one or moretemperature-altering devices operable to receive a signal and initiate asequence to alter the temperature in one or more zones, if theinterpreted real-time ORP does not conform to an optimized ORP setting,wherein the optimized ORP setting relates to the dynamic and inhibitsdeposition or effectuates release of at least a portion of said depositinto the water of the hot water system.